A broad-band λ/4 plate whose wavelength dispersibility is controlled to the reciprocal wavelength dispersion is useful in the optical field. A manufacturing method of such a broad-band λ/4 plate, a method of manufacturing by uniaxial stretching with a polymer film obtained by copolymerization of a monomer unit having positive refractive index anisotropy and a monomer unit having a negative birefringence property is proposed (e.g., refer to WO 00/2675). However, the film obtained by this method is uniaxial, and manufactured by stretching of a polymer film, so that the film thickness is thick, dimensional stability is inferior, and the optical performances are susceptible to humidity and heat, therefore, the improvement of these points has been required.